Constant-factor approximation of MinCostCSP with a conservative majority polymorphism

Marcin Kozik; Stanislav Živný

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arXiv · 2607.10667

Constant-factor approximation of MinCostCSP with a conservative majority polymorphism

Marcin Kozik·Stanislav Živný

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Abstract

For a relational structure A, the Minimum Cost Constraint Satisfaction Problem is the following problem denoted by MinCostCSP(A): Given an instance of CSP(A) with rational costs on variable-value pairs, find a solution to the instance minimizing the sum of the chosen costs. For the exact minimization, a classification of MinCostCSP(A) in terms of A was established by Takhanov [STACS'10]. We focus on constant-factor approximations of MinCostCSP(A). DeHaan, Huang, and Lee recently showed that if A fails to admit a conservative near-unanimity polymorphism then MinCostCSP(A) is not constant-factor approximable [APPROX'25]. We provide a first step towards a classification, by proving a dichotomy for structures A admitting a conservative majority (also known as 3-near-unanimity) polymorphism. Our dichotomy criterion is not in terms of an algebraic condition on A but we show that this is unavoidable. We include a simple argument proving that no such condition exists.

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Marcin Kozik, Stanislav Živný. 2026-07-12. Constant-factor approximation of MinCostCSP with a conservative majority polymorphism. https://arxiv.org/abs/2607.10667

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